curl_global_cleanup().  Update corresponding man pages...

Improve the logic in curl_global_cleanup() and curl_global_init() so that
they are not called twice if the application libraries have been
initialized and make sure to reset the init flags in curl_global_cleanup().

first resume was used on all files instead of being reset between each file.
As found by Björn Stenberg.

but it shows good manner to always cleanup

explicitly, as they're taken care of indirectly by curl/curl.h these
days.

than 509 letters (as newer gcc warns on with -Wall)

screw a few things up.

are optional...

made the big config struct local (big . => -> replace)